Actuator of a parking brake

ABSTRACT

An actuator for a parking brake of a motor vehicle is provided, which includes an electric motor ( 1 ) whose rotor ( 20  has a threaded spindle ( 3 ) on which a spindle nut ( 4 ) is located. Between the threaded spindle ( 3 ) and the spindle nut ( 4 ), rolling bodies are in rolling engagement with threaded paths ( 6, 7 ) formed on the spindle nut ( 4 ) and on the threaded spindle ( 3 ). A cable pull ( 8 ) for actuating a brake acts upon the spindle nut ( 4 ).

BACKGROUND

The present invention relates to an actuator for a parking brake of amotor vehicle. Parking brakes actuated with an actuator can be setautomatically when parking and can be released automatically whenstarting to move again. These parking brakes can also be designated asactive parking brakes.

These usually electromechanical actuators comprise an electric motor,which sets the parking brake via a control element. The control elementcan comprise gearing. These actuators should enable quick release andapplication of the parking brake. The objective of the present inventionis to provide an actuator of a parking brake for a motor vehicle, whichhas a simple design and can be actuated reliably.

SUMMARY

The actuator according to the invention from claim 1 has the advantagethat the rotor of the electric motor drives the threaded spindledirectly, so that gearing between the rotor and the threaded spindle iseliminated. The known spindle nuts arranged on the threaded spindleoperate with very low friction, because relative rotation between thespindle nut and the threaded spindle is performed with the rolling ofrolling bodies on threaded paths of the spindle nut and the threadedspindle. The combination of the direct drive and rolling body threadeddrive enables a drive with very high mechanical efficiency. The spindlenut interacting with the threaded spindle form a known rolling bodythreaded drive, which operates reliably. The actuator according to theinvention has a compact and economic design due to the elimination ofintermediate gearing. Due to the low friction losses, the electric motorcan be small.

The spindle nut is displaced in the axial direction when the threadedspindle rotates, because a rolling body threaded drive represents arotary transmission gearing. The cable pull attached to the spindle nutis tightened by the axial displacement of the spindle nut throughtensioning. Loosening is realized through an opposite movement of thespindle nut.

The actuator according to the invention enables a biasing force of about1600 N per wheel side. The tension path—thus the travel path of thespindle nut—can equal approximately 25 mm. The activation time can bereduced to about 700 milliseconds at a spindle rpm of approximately 1250revolutions/min. Quick activation times are therefore possible.

If the parking brake is activated, thus the actuator has been set, thevehicle is secured. If there is not a self-locking gear between theelectric motor and the cable pull, then a locking device can beprovided, which secures the rotor and/or the threaded spindle againstrotation. This locking can be realized preferably in a mechanical way,for example, through positive-fit meshing of locking elements, of whichone is fixed in rotation on the rotor and the other is fixed in therotational directions of the rotor. For example, a displaceable pistoncan engage in a gap of a gear defined by teeth. The tensile load of thecable pull can exert a torque on the threaded spindle or the rotor. Thistorque is then received by the locking device. In the case of thepiston, a tooth then presses against the piston. The piston is then heldtight and rotation of the spindle nut is stopped.

If the parking brake is to be released, first the cable pull is relaxedby actuating the electric motor, which has the result that the piston isno longer held tight. If a spring force is applied to the piston, thepiston can be moved out from its locking position under this springforce. The parking brake is then released.

If the parking brake is to be released, but the electric motor cannot beused due to loss of power, an emergency unlocking device is provided.With this emergency unlocking device, which can be operated, forexample, by hand, the locking device can be disabled. For the lockingdevice described as an example, it is necessary to remove the load ofthe toothed disk which is pressed against the piston, so that the pistoncan spring out of its locking position under the spring force. With theemergency locking device, now a torque is exerted by hand, whichcounteracts a torque exerted by the load of the cable pull. This meansthat the pressure is taken off the piston, so that the piston can springout. The parking brake is then released.

If, for example, the emergency unlocking device has a band, which wrapsaround the toothed disk and which, in the wrap-around area has a pocket,into which the teeth of the toothed disk project, first the toothed diskcan rotate without coming into locking contact with the band. If theband is provided with a crosspiece, which can engage in a gap of thetoothed disk, the emergency unlocking device can operate as follows.With one end, the band is fixed to a tension spring. At the other end itis now tightened. The band now moves along the periphery of the tootheddisk, wherein the crosspiece engages in the gaps. For further movementof the band, the toothed disk is taken along and the piston of thelocking device relaxes, so that this piston can spring out from the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference to anembodiment shown in a total of three figures. Shown are:

FIG. 1 a perspective view of an actuator according to the invention fora parking brake of a motor vehicle,

FIG. 2 a longitudinal section view of a part of the actuator accordingto FIG. 1, and

FIG. 3 another perspective view of the actuator according to theinvention from FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The actuator according to the invention shown in FIGS. 1 and 3 for aparking brake of a motor vehicle is provided with an electric motor 1,having a rotor 2 with a threaded spindle 3. A spindle nut 4 is arrangedon the threaded spindle 3. The spindle nut 4 is shown clearly in FIG. 2in a longitudinal section. It should be noted from FIG. 2 that betweenthe threaded spindle 3 and the spindle nut 4 there are rolling bodies 5in rolling engagement with threaded paths 6, 7 formed on the spindle nut4 and the threaded spindle 3. The spindle nut 4 and the threaded spindle3 form a ball screw 9, wherein the rolling bodies are formed by balls 5a, which circulate in endless ball raceways 10. The ball raceways 10 aredefined by the threaded paths 6, 7 of the threaded spindle 3 and thespindle nut 4. The rotor 2 has two opposite ends, which are arranged ontwo sides of a motor housing 1 a of the electric motor 1. One of thethreaded spindles 3 is attached to both ends of the rotor 2. Thisthreaded spindle 3 is coaxial to the rotor 2 and locked in rotation withthis rotor. These two threaded spindles 3 have threaded path sections ofopposing slope. A spindle nut 4 is arranged on each threaded pathsection. A cable pull support 4 a is fixed to each spindle nut 4. Cablepulls 8 are suspended in the two cable pull supports 4 a. The cablepulls 8 each engage one of the parking brakes of the motor vehicle. Theparking brakes are not shown here. FIG. 3 shows that the cable pullsupports 4 a are arranged displaceable along a connecting member 26 hereshown only with dashed lines. This connecting member 26 is used as arotational lock for the cable pull supports 4 a and the spindle nut 4.

FIG. 3 further shows a locking device 11, which prevents rotation of therotor 2 and thus of the threaded spindle 3 when no current flows to theelectric motor 1. This locking device 11 has a first locking element 12fixed in rotation with the rotor 2 and a movable second locking element13, wherein, in the locking position the two locking elements 12, 13engage with a positive fit in each other for preventing rotation of therotor 2. The first locking element 12 has a toothed disk 15 locked inrotation with the rotor 2. Several teeth 16 distributed over the extentof the disk form gaps 17 on the periphery of this toothed disk.

The locking device 11 further comprises a frame-fixed electromagnet 14,which is provided with the second locking element 13. The lockingelement 13 moves into the locking position under the activation of theelectromagnet 14, wherein the locking position is reached when thesecond locking element 13 engages in the gap 17. The second lockingelement 13 is here formed by a piston 18. The piston 18 is acted on by aspring force and can be pushed against the spring force into the lockingposition through the activation of the electromagnet 14.

The ball screw 9 forms a control element, which is driven by the rotor2. Instead of the ball screw, other rotary transmission gears are alsopossible.

FIG. 3 further shows an emergency unlocking device 19 for relaxing thelocking device 11 from a load applied for tensioning the brake.

This emergency unlocking device 19 has a band 20, which is arrangedperpendicular to the rotor axis and which wraps around a contact surface21 arranged coaxial to the rotor axis. This contact surface 21 is formedon the toothed disk 15 and axial to two sides of the teeth 16. The band20 has legs or belts 23 extended in the longitudinal direction of theband 20, wherein the belts 23 can be brought into contact with thecontact surface 21. The two legs or belts 23 define a large pocket 24,which is bordered by a catch 22 along the band. This catch 22 is formedin the present example as a transverse crosspiece 22 a, which connectsthe two belts 23 to each other. One band end is attached to a tensionspring 27, which is supported, on its side, by a housing 25 fixed to theframe. The other band end engages a cable pull 28. By tensioning thecable pull 28, the band 20 contacts the contact surface 21 of thetoothed disk 15 with its belts 23 and is moved relative to the tootheddisk 15 in the counterclockwise direction, wherein this band is movedunder deflection of the tension spring 27.

In the following, the function of the actuator according to theinvention is described. For activating the not-shown parking brakes, theelectric motor 1 is activated. Through rotation of the rotor 2 and thethreaded spindles 3, spindle nuts 4 are displaced in the axial directionalong the threaded spindle 3, that is, in the direction towards themotor housing 1 a. Under this displacement of the cable pull support 4a, the cable pulls 8 are tensioned, wherein, as a result of activatingthe cable pulls 8, the parking brakes are activated. If there is nocurrent flowing to the electric motor 1, the piston 18 of the lockingdevice 11 moves into the closest possible gap 17. The toothed disk15—and thus the rotor 2—is now engaged and locked in its rotationalposition.

For releasing the parking brake, first the piston 18 must be moved againout of the gap 17. However, at first this can be made more difficult inthat under a torque acting on the toothed disk 15, one of the two teethadjacent to the piston 18 presses against the piston 18. For relaxingpressure, the electric motor 1 can be activated for a short time oroptionally the emergency unlocking device 19 can be activated, if, forexample, the electric motor 1 has failed. For this purpose, for example,in the passenger compartment there can be a handle attached to the cablepull 28 in order to be able to pull on the cable pull 28. The band 20 isnow pushed under the section of the cable pull 28. The catch 22 of theband 20 shown in FIG. 3 is finally led into a gap 17. For furthermovement of the band, now the toothed disk 15 is now taken along bymeans of a positive engagement. Under these positive engagementmeasures, the piston 18 is now released from pressure. Finally, thepressure is reduced so far that the piston 18 springs back under thespring force and is led out of engagement with the gap 17. Now, thetoothed disk 15 can rotate again, that is, also the rotor 2 and thethreaded spindle 3. Now, the spindle nuts 4 can be displaced away fromthe motor housing 1 a along the threaded spindle 3 under the relaxing ofthe cable pulls 8, whereby the parking brakes are released.

LIST OF REFERENCE SYMBOLS

-   1 Electric motor-   1 a Motor housing-   2 Rotor-   3 Threaded spindle-   4 Spindle nut-   4 a Cable pull support-   5 Rolling body-   5 a Ball-   6 Threaded path-   7 Threaded path-   8 Cable pull-   9 Ball screw-   10 Ball raceway-   11 Locking device-   12 Locking element-   13 Locking element-   14 Electromagnet-   15 Toothed disk-   16 Tooth-   17 Gap-   18 Piston-   19 Emergency unlocking device-   20 Band-   21 Contact surface-   22 Catch-   22 a Transverse crosspiece-   23 Belt-   24 Pocket-   25 Housing-   26 Connecting member-   27 Tension spring-   28 Cable pull

1. Actuator for a parking brake of a motor vehicle, comprising anelectric motor (1), having a rotor (2) with a threaded spindle (3), onwhich a spindle nut (4) is arranged, wherein between the threadedspindle (3) and the spindle nut (4) there are rolling bodies (5) inrolling engagement with threaded paths (6, 7) formed on the spindle nut(4) and the threaded spindle (3), and wherein a cable pull (8) engagesthe spindle nut (4) for activating a brake.
 2. Actuator according toclaim 1, wherein the threaded spindle (3) is arranged coaxial to therotor (2) and is provided with a second threaded path section ofopposite slope, wherein another spindle nut (4) is arranged on thesecond threaded path section and wherein another cable pull (8) engageson the second spindle nut (4) so that cable pulls are engaged on each ofthe spindle nuts.
 3. Actuator according to claim 1, wherein ball screws(9) are used, wherein the rolling bodies are formed by balls (5 a),which circulate in endless ball raceways (10), which are defined by thethreaded paths (6, 7) of the threaded spindle (3) and the spindle nut(4).
 4. Actuator according to claim 1, wherein a locking device (11) isprovided, which prevents rotation of the rotor (2) and thus the threadedspindle (3) when no current flows to the electric motor (1).
 5. Actuatoraccording to claim 4, wherein the locking device (11) has a firstlocking element (12) fixed in rotation with the rotor (2) and a movablesecond locking element (13), wherein in a locking position the twolocking elements (12, 13) engage each other with a positive fit forpreventing rotation of the rotor (2).
 6. Actuator according to claim 5,wherein an electromagnet (14) fixed to the frame acts on the secondlocking element (13), which moves into the locking position throughactivation of the electromagnet (14).
 7. Actuator according to claim 5,wherein the first locking element (12) has a toothed disk (15) fixed inrotation with the rotor (2) and on whose periphery several teeth (16)are distributed having gaps (17) provided therebetween.
 8. Actuatoraccording to claim 5, wherein the second locking element has a piston(18) for engagement with the first locking element (12).
 9. Actuatoraccording to claim 8, wherein a spring force acts on the piston (18),wherein the piston (18) is moveable against the spring force into thelocking position.
 10. Actuator according to claim 7, wherein the piston(18) engages in one of the gaps (17) of the toothed disk (15) in thelocking position of the locking device (11).
 11. Actuator for a parkingbrake of a motor vehicle, comprising an electric motor (1), having arotor (2) that drives a control element, wherein a locking device (11)is provided for positive-fit locking of the actuator, and with anemergency unlocking device (19) for relaxing the locking device (11)from a load applied for applying the brakes.
 12. Actuator according toclaim 11, wherein the emergency unlocking device (19) has a band (20),which is arranged perpendicular to the rotor axis and which wraps arounda contact surface (21) arranged coaxial to an axis of the rotor. 13.Actuator according to claim 12, wherein the band (20) is provided with acatch (22) for active engagement with a counter catch (17) locked inrotation to the rotor (2), wherein, in active engagement, the band (20)prevents rotational movement of the rotor (2).
 14. Actuator according toclaim 13, wherein the band (20) is arranged for movement in alongitudinal direction.
 15. Actuator according to claim 13, wherein therotor (2) is provided with a toothed disk (15), having several teeth(16) distributed over a periphery thereof, the periphery including gaps(17) formed between the teeth, wherein, in active engagement, the catch(22) of the band (20) engages in one of the gaps (17) forming thecounter catch.
 16. Actuator according to claim 15, wherein the band (20)has a pocket (24), which is defined by a belt (23) arranged in alongitudinal direction of the band (20) and by the catch (22) and inwhich the teeth (16) of the toothed disk (15) engage.
 17. Actuatoraccording to claim 1, wherein a housing (25) of the actuator is providedwith a connecting member (26), on which the spindle nut (4) is locked inrotation.
 18. Actuator according to claim 11, wherein the controlelement is formed by a ball screw (9) or other rotary transmissiongearing.